Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Net income	$ 3,996	$ 9,029
Other comprehensive income (loss):
Foreign currency translation adjustment	679	3,078
Adjustment to retirement benefit liability, net of tax	(3)	(1)
Adjustment to post employment health care benefit liability, net of tax	29	38
Other comprehensive income	705	3,115
Total comprehensive income	$ 4,701	$ 12,144